Induction of water repellency by leaves of contrasting Australian native species: effects of composition and heating

Abstract

Aims This study identifies the contribution of leaf matter from individual plant species on water repellency with a focus on the composition of organic compounds and the role of heat in releasing these compounds to soil. Methods Leaf powder from four plant species (Banksia menziesii, Eucalyptus marginata, Allocasuarina fraseriana, Xanthorrhoea preissii) was mixed with acid-washed sand (AWS) under a range of temperatures and WR measured. Plant chemical composition was characterized by extraction of leaf powder and GC/MS analysis. Results Increasing concentrations of plant powder mixed with AWS increased WR for three species; whereas for X. preissii there was no WR at any concentration. Heating increased WR for all species over the range of 30 to 120 °C. B. menziesii had the greatest WR, which was associated with the largest diversity of fatty acids and n-alcohols and highest concentration of alkanes, whereas X. preissii with the smallest WR had only C16 alcohol and C16 fatty acids at relatively low concentration. Conclusions Physically mixing leaf powder with AWS allows the contribution of different plant species on WR to be directly examined. WR appears to be related to differences in the concentrations and diversity of n-alcohols, n-fatty acids, and high n-alkanes in the leaves. The observed temperature effects on WR provide insights into the kinetics of release and dispersal of organic compounds from interstitial material.

Alterations in aggregate characteristics of thermally heated water-repellent soil aggregates under laboratory conditions

“…These results are comparable with Novák et al (2009), who reported a decline in SWR with increasing temperature in Meadow and Pine Forest soils. Dao et al (2022) and Doerr et al (2005) also reported an increase in SWR with increasing temperature up to about 150 °C, following a decline in SWR with heating beyond 150 °C.…”

“…In general, the organic matter contents of aggregates decreased with increasing depth, TH, and ED. Soil organic matter is crucial for the occurrence of SWR under both burned and unburned conditions (Atanassova and Doerr, 2010;Dao et al, 2022). In our study, we evaluated the relationship between soil organic matter content and SWR by examining contact angles (Figure 6).…”

“…However, the reports on temperature levels and conditions that are associated with increment, decline, or elimination in SWR are contradictory. Several reports show that SWR increases with increasing temperature for the ranges of 100-150 °C (Zavala et al, 2010), 50-150 °C (Dao et al, 2022;Doerr et al, 2005), and25-220 °C (García-Corona et al, 2004). Doerr et al (2005) reported that SWR starts to decrease at 200 °C, while Zavala et al (2010) stated that SWR decreases at about 250 °C.…”

“…The presence of organic materials in the soil, as coatings on soil mineral grains and intermixed materials, causes water-repellent conditions. Many factors influence water-repellent conditions, including the content and the composition of organic carbon (Atanassova and Doerr, 2010;Dao et al, 2022), fungal activities, pH (Lin et al, 2006), temperature (Zavala et al, 2010), humidity levels (Whelan et al, 2014), and soil moisture levels (Caltabellotta et al, 2022;Kajiura et al, 2012). The immediate impact of SWR is the hindrance of water infiltration into the soil, consequently causing increased overland flow and topsoil erosion (Butzen et al, 2015).…”

“…There are pieces of evidence available to show that the heat generated by wildfire can either increase, decrease, or eliminate the SWR conditions (Doerr et al, 2006;Zavala et al, 2010). The impact of heat on underlying soils depends on many factors such as the intensity and the severity of fire (Doerr et al, 2006), associated peak soil temperature (Zavala et al, 2010), the duration of exposure to that temperature peaks (Dao et al, 2022;Doerr et al, 2004), rising rate of temperature (Bruns et al, 2020), and moisture levels during heating (Zavala et al, 2010). However, the reports on temperature levels and conditions that are associated with increment, decline, or elimination in SWR are contradictory.…”